The fire alarm unit of the invention is advantageous in that it can be sold at a relatively low price, and a number of the units may be purchased and mounted in the various rooms of residences, hotels and offices. The alarm unit is battery operated and does not depend for its energy on the electrical mains which could fail during a fire.
As stated above, the alarm unit is held in its normally inactive state by a strip of cermet, or like material. Cermet is a group of composite materials consisting of an intimate mixture of ceramic and metallic components. Selected metallic and ceramic components may be used to provide a cermet which will melt and fail at a selected temperature of around, for example, 150.degree. F., which is indicative of a fire condition. Representative cermets are as follows:
______________________________________ Representative cermets Class Ceramic Metal addition ______________________________________ Oxides Al.sub.2 O.sub.3 Al, Be, Co, Co--Cr, Fe, stainless steel Cr.sub.2 O.sub.3 Cr MgO Al, Be, Co, Fe, Mg SiO.sub.2 Cr, Si ZrO.sub.2 Zr UO.sub.2 Zr, Al, stainless steel Carbides SiC Ag, Si, Co, Cr TiC Mo, W, Fe, Ni, Co, Inconel, Hasiel- loy, stainless steel, Vitallium WC Co Cr.sub.3 C.sub.2 Ni, Si Borides Cr.sub.3 B.sub.2 Ni TiB.sub.2 Fe, Ni, Co ZrB.sub.2 Ni Silicides MoSi.sub.2 Ni, Co, Pt, Fe, Cr Nitrides TiN Ni ______________________________________
A selection may be made from the above list for the desired temperature characteristics for application to the fire alarm of the present invention.